Power semiconductor devices are commonly required to achieve a high reverse voltage blocking capability. Some applications require power semiconductor devices to withstand reverse voltages of 200 volts or greater.
Edge termination structures have been incorporated into power semiconductor devices to improve reverse voltage blocking capability. Edge termination structures typically surround the active device region that includes the power semiconductor devices, and may be near the edge of the substrate. Edge termination structures mitigate avalanche breakdown, and hence improve reverse voltage blocking capability, by redirecting equipotential lines within the drift region of the device toward the main surface and away from the edge of the substrate.
Edge termination structures may include trenches having buried electrodes that are electrically connected to a doped region adjacent the trench and at the surface of the substrate. This adjacent doped region forms a p-n junction with an oppositely doped subjacent region. Typically, the connection between the buried electrode and the adjacent doped region is provided by a contact that is formed over the buried electrode and in a recessed portion of the adjacent semiconductor substrate. A silicide layer or other conductive material may be provided in the recessed portion between the contact and the semiconductor to improve electrical connectivity. Because of the recess, the silicide layer is spaced close to the p-n junction. Subsequent thermal processing of the device, e.g. due to platinum diffusion for lifetime carrier reduction, inter-layer dielectric deposition, etc., causes the silicide layer to diffuse deeper into the semiconductor body toward the second doped region. If the silicide layer diffuses deep enough it will short the p-n junction between the first and second doped regions, causing substantial leakage. Devices with high leakage are discarded, reducing yield.